This application is based upon and claims priority from Japanese patent application Nos. Hei 10-300809, filed Oct. 22, 1998 and Hei 11-124904, filed Apr. 30, 1999, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel supply system which relieves fuel pressure pulsations in a fuel line of an internal combustion engine such as a direct injection engine which directly injects fuel into a cylinder.
2. Description of Related Art
According to a direct injection engine, it may inject fuel into a highly pressurized cylinder at a compression stroke. Therefore, pressure of fuel supplied to an injector is set higher than that of a conventional engine which injects fuel into an intake port having a low pressure.
The fuel is intermittently discharged to a common high pressure fuel pipe at a fuel discharge pump, such as a fuel injection pump, by a plunger which is driven by a cam to reciprocate. Accordingly, high pressure pulsation is generated in fuel in the high pressure fuel pipe according to the shape of the cam. In addition, the pressure in the high pressure fuel pipe is temporarily reduced because each one of a plurality of injectors connected to the common high pressure fuel pipe intermittently opens its valve respectively to inject fuel. As a result, pressure pulsations having high pressure and low pressure are generated in fuel flowing in the high pressure fuel pipe, and proceed in the high pressure fuel pipe as pressure waves.
Accordingly, whether the pressure pulsation having high pressure or the pressure pulsation having low pressure is at a fuel supply port of an injector when the injector opens its valve changes fuel injection quantity even if the injector opens its valve at the same timing.
Such injection quantity fluctuation caused by the pressure pulsation in the high pressure fuel pipe is also generated on the conventional engine which injects fuel into the intake port as long as a plurality of injectors are connected to a common fuel pipe to receive fuel. In order to solve this problem, JP-U-57-100,693 discloses a pressure relaxation device, that is a pressure damper.
However, an injection pressure of the injector and a fuel pressure in the fuel line for the direct injection engine are higher than those for the conventional engine. Therefore, such injection quantity fluctuation for each one of the injectors for the direct injection engine may be greater.
If a conventional pressure damper comprising a soft damping member, such as a diaphragm or a bellows, is applied to a high pressure fuel pipe of the direct injection engine, the damping member may be easily broken because the fuel pressure in the high pressure fuel pipe of the direct injection engine is high. In that case, sufficient durability and reliability can not be obtained. If a full accumulator is employed in order to relieve the pressure in the high pressure fuel pipe of the direct injection engine, the whole apparatus is increased in size and cost because the accumulator itself is large and expensive.
According to a V-type engine, single fuel line is separated into two pipes toward two banks and joined together at their ends to form a loop. According to such loop-shaped fuel line, a crests or troughs of the pressure waves progressing in the respective separated fuel pipes may meet at the joint of the pipes. In that case, the pressure pulsation is magnified by summating respective crests or respective troughs, and a big pressure wave progresses in the fuel line in a reversed direction.
Furthermore, the pressure pulsation is magnified by resonance when a pressure pulsation frequency approaches a natural frequency of the fuel line.
Such magnified pressure pulsations may cause further fluctuation of the injection quantity.
JP-A-10-73,062 discloses an apparatus which absorbs the vibration by a resonator. However, the resonator makes the structure complicated and expensive. Furthermore, the pressure pulsation in a wide range of the frequency can not be prevented by absorbing pressure pulsation in a certain range of the frequency because the engine rotation speed always varies and the generated pressure pulsation and frequency also vary.
Further, JP-A-9-170514 discloses an accumulator injection apparatus for a diesel engine having a common-rail for cylinders at a part of a fuel passage connecting a high pressure supply pump and fuel injection valves for respective cylinders, and having an orifice at an inlet or outlet of the common-rail to prevent the fuel pressure pulsation. However, if such apparatus is applied to a direct injection engine using gasoline, vapors are prone to remain in the fuel because the diameter of the orifice is very small. As a result, it is difficult to supply small amount of fuel precisely according to the reducing injection quantity during the lean burn. Furthermore, the small diameter of the orifice may be clogged by a foreign object.
The present invention is made in light of the foregoing problem, and it is an object of the present invention to provide a fuel supply system which reduces pressure pulsation in a high pressure fuel pipe and which has high durability and reliability.
According to an aspect of the present invention, when a high pressure portion of a pressure wave in a high pressure pipe reaches an inlet of a damping chamber formed in a pressure relaxation device, a valve provided at the inlet of the damping chamber opens to receive and hold the high pressure portion in the damping chamber.
Accordingly, the pressure around the inlet is reduced, and a reflection of the high pressure portion in a reverse direction is prevented.
Then, when a low pressure portion of the pressure wave reaches the inlet of the damping chamber, the high pressure portion held in the damping chamber is gradually released via a restricted orifice. Accordingly, the pressure of the low pressure portion increases, and a reflection of the low pressure portion in a reverse direction is prevented.
Thus, the pressure pulsation generated in fuel in the high pressure pipe is reduced, and an injection quantity for a valve opening unit time of the injector becomes constant. Accordingly, it becomes possible to reduce a fluctuation of the injection quantity even if the engine speed is changed.
Furthermore, the pressure relaxation device includes the damping chamber, the valve for opening/closing the inlet of the damping chamber, an elastic member for applying a spring force to the valve, and the restricted orifice which bypasses the valve. Accordingly, a breakage is prevented even if the fuel pressure is high in the high pressure pipe, and high reliability is obtained because of a high durability of the system.
Furthermore, the pressure relaxation device may be formed as an extended high pressure pipe, thereby facilitating to reduce its size. Therefore, the fuel supply system or the engine itself is not increased in size by providing the pressure relaxation device.
According to another aspect of the present invention, the restricted orifice is formed in the valve. Accordingly, manufacturing the restricted orifice is facilitated.
According to another aspect of the present invention, the restricted orifice is formed as a gap between a valve body and a valve seat by a spacer which prevents a fully closed state. Accordingly, it is not necessary to bore a hole.
According to another aspect of the present invention, the restricted orifice is formed in the valve seat on which the valve body abuts.
According to another aspect of the present invention, when a high pressure portion of a pressure wave transmitted in the fuel in the high pressure fuel pipe reaches an inlet of a damping chamber formed in a pressure relaxation device, a flexible bag enclosing a high pressure gas is slightly deformed to absorb the high pressure portion of the pressure wave. Further, when a low pressure portion reaches the inlet of the damping chamber, the flexible bag returns to its original shape to increase the pressure of the low pressure portion, thereby reducing the pressure pulsation of the fuel in the high pressure pipe.
Accordingly, a fluctuation of an injection quantity of the injector is prevented. Since the pressure relaxation device is like an extended high pressure pipe, it is easy to reduce it in size. Thus, the fuel supply system or the engine will not be increased in size by providing the pressure relaxation device.
According to another aspect of the present invention, the bag for absorbing the pressure pulsation is made of a rubber reinforced with a fiber which is slightly extendable. Thus, it has a very strong structure.
According to another aspect of the present invention, the bag is filled with inert gas. Accordingly, deterioration of the bag caused by a gas is prevented.
According to another aspect of the present invention, it is suitable for a multi-cylinder V-type engine because the high pressure pipe is formed in the shape of a loop.
According to another aspect of the present invention, it is suitable for a multi-cylinder in-line engine because the high pressure fuel pipe has a first end and a second end. However, it may be applicable to a multi-cylinder V-type engine if the high pressure fuel pipe is bent.
According to another aspect of the present invention, a method of designing a fuel supply system for an internal combustion engine which reduces the pressure pulsation of fuel includes a step of calculating a resonance frequency corresponding to a predetermined design data of the system, and includes a step of changing the design data such that the calculated resonance frequency exceeds a target frequency determined based on an order frequency of harmonics which may cause the resonance, and includes a step of calculating a waveform of the pressure pulsation by a numerical analysis, and includes a step of determining an order frequency of the harmonics, whose resonance should be prevented, from a peak if an amplitude of the calculated waveform, and includes a step of calculating a magnitude of a pulsation pressure, and includes a step of changing design data of the system such that the pulsation pressure is less than a predetermined target value.
Accordingly, the occurrence of the resonance is completely prevented without overlooking any order frequency.
According to another aspect of the present invention, a pair of protruded portions having an inner diameter greater than an inner diameter of a connecting pipe are formed on a pair of delivery pipes opposite to each other, and the delivery pipes are connected by attaching a connecting pipe to the protruded portions.
Accordingly, an average inner diameter of a connecting portion is greater than that of the connecting pipe, and the protruded portions are formed opposite to each other. Thus, the length of the connecting pipe is shortened by the length of the protruded portions. Accordingly, the resonance frequency (natural frequency) of the system is shifted to higher side, and a possibility of the conformity with a discharge pulsation of a fuel pump or with its harmonics is reduced. Therefore, a pressure pulsation increase of the high pressure fuel flowing in the fuel pipe caused by the resonance is prevented, and an injection quantity fluctuation of each injector is prevented.
According to another aspect of the present invention, an enlarged volume portion whose inner diameter is enlarged is provided on a connecting pipe connecting delivery pipes. Accordingly, an average inner diameter of the connecting pipe is increased, and the resonance frequency of the system shifts to the higher side. Thus, the resonance caused by the conformity with the pressure pulsation or the frequency of its harmonics is prevented.
According to another aspect of the present invention, a part of a connecting pipe connecting delivery pipes is made of a flexible material. Thus, the connecting pipe is bent with smaller force, and thereby facilitating the assembly of the fuel supply system. Furthermore, the flexible material absorbs and reduces the pressure pulsation of the high pressure fuel by its elastic deformation, and the flexible material prevents a possible damage of the connecting pipe caused by vibration fatigue for a rigid body.
According to another aspect of the present invention, a pair of delivery pipes corresponding to a pair of banks are connected in series by a connecting pipe, one of the delivery pipes having a volume that is greater than a volume of the other of the delivery pipes, such that widths of respective pressure pulsations in the delivery pipes are substantially equal. Accordingly, fuel injection quantity fluctuation between the cylinders of the respective banks, caused by a difference between the pulsation widths of the pressure pulsations, is prevented.
According to another aspect of the present invention, an inside of a pair of delivery pipes is divided into a plurality of groups. Accordingly, the resonance frequency of the entire system shifts to the higher side because the resonance frequencies (natural frequency) in respective groups are increased. Thus, a possibility of an occurrence of the resonance with the pressure pulsation of the discharge pulsation and the like or its harmonics is reduced. Since the divided groups communicate with an adjacent one of the divided groups via a narrow passage, the flow of the high pressure fuel among the divided groups is not prevented.
According to another aspect of the present invention, a connecting pipe having a relatively large diameter is unified with a delivery pipe. Accordingly, an impedance of a connecting portion and an impedance of the entire system are reduced, and the resonance frequency (natural frequency) of the system extremely shifts to the higher side. Thus, a possibility of the synchronization with the pressure pulsation or frequency of its harmonics is reduced, and the resonance under the normal driving condition of the engine is prevented.
According to another aspect of the present invention, at least one pair of delivery pipes adjacent each other are connected via a flexible member on their substantially entire surfaces opposing each other. Accordingly, impedance of the delivery pipes is decreased.
According to another aspect of the present invention, a directional restricted orifice is provided on at least a part of a connecting pipe as a high pressure pipe connected to an injector. The flow resistance at the restricted orifice is decreased when pressurized fuel flows from a fuel pump toward the injector, but it is increased when pressurized fuel flows in an opposite direction. Thus, when a pressure wave, generated by a discharge pulsation of the fuel pump or opening/closing of the injector, progresses in the high pressure pipe in the opposite direction, the restricted orifice reduces its opening area to prevent the pressure wave progress. Accordingly, an amplitude increase caused by superposition or resonance of the pressure waves is prevented.
According to another aspect of the present invention, the directional restricted orifice includes a conical elastic body having a flexible opening on a tip of the conical elastic body.
According to another aspect of the present invention, a fuel pump includes a plurality of plungers slidably inserted in respective cylinders, a common cam for reciprocating the plungers, a plurality of pressure chambers formed by the cylinders and the plungers, and a common discharge chamber for mixing pressurized fuel discharged from the pressure chambers. Relative angle positions of the respective cylinders are determined such that pressure pulsations of the pressurized fuel generated in the respective pressure chambers are canceled each other in the common discharge chamber.
Accordingly, discharge pulsation is not substantially included in pressurized fuel discharged from the common discharge chamber. Thus, a fuel injection quantity fluctuation of the injectors for respective cylinders and a vibration occurrence are prevented.